Indexing and searching of electronic message transmission thread sets

ABSTRACT

A method includes describing the thread configurations of a volume of well-ordered electronic message transmissions (EMT) and utilizing the thread configuration data to conduct selective searches of the EMT volume. An apparatus includes a thread processor and a query manager. The thread processor analyzes the EMT threads and records the thread configuration data. The query manager utilizes the thread configuration data to conduct selective searches of the EMT volume.

FIELD OF THE INVENTION

The present invention relates to the processing of electronic textgenerally.

BACKGROUND OF THE INVENTION

Since its introduction to the public in the late 20^(th) century, emailhas become a popular and widely used form of communication both at homeand in the workplace. In addition to the advantages email introduced tothe realm of interpersonal communications, by making the delivery ofwritten messages quicker and more convenient, email further introducedcompletely new benefits to the exchange of written messages.

For example, the “Reply” and “Forward” functions available to emailusers introduced the “discussion thread”. Reference is now made to FIG.1, which depicts an email exchange process 19 by which a discussionthread is formed. An email discussion thread is started by thetransmission of a single email message 10 (the root message), fromPerson X to Person Y, as indicated by arrow 13. The content of email 10is the text 20 written by Person X. This initial email transmission isdefined as Round 1 of email exchange 19.

Person Y then replies, as indicated by arrow 15, to Person X, by using aconventional email “Reply” function. Use of the “Reply” functiongenerates email 11, which contains root message text 20, and to whichPerson Y adds his reply text 21. This first reply is defined as Round 2of email exchange 19.

Person X then replies to Person Y using the “Reply” function, asindicated by arrow 17, in which case his reply email 12 contains rootmessage text 20, first reply text 21 and new reply text 22. This secondreply is defined as Round 3 of email exchange 19.

One benefit of the email discussion thread is that it provides runningdocumentation of a discussion occurring between two or more people. Atany time it is possible to read the entire discussion thread beginningfrom the root message, and thus obtain a full picture of what wasdiscussed, and which contributions to the discussion were made by whom,without a laborious search for documents.

Unfortunately, discussion threads significantly increase the volume ofmessages to be stored and processed by an email administration system.For example, the processes of indexing and searching message volumesbecome increasingly cumbersome with increasing message volume size.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is an illustration of the creation of a discussion thread duringan exchange of emails;

FIGS. 2, 3 and 4 are detailed exemplary representations of the emailsintroduced in FIG. 1;

FIG. 5 is an illustration of an innovative search engine constructed andoperative in accordance with a preferred embodiment of the presentinvention;

FIG. 6 is an exemplary conjoined email thread set;

FIG. 7 is a graphical illustration of the tree-like structure of theconjoined thread set introduced in FIG. 6;

FIG. 8 is a block diagram illustration of the details of the threadprocessor of FIG. 5;

FIGS. 9 and 10 are detailed representations of the exemplary compactemail volumes of FIG. 8;

FIGS. 11 a and 11 b are graphical illustrations of the root lookup andlast offspring data for the exemplary compact email threads of FIGS. 9and 10;

FIG. 12 is a graphical illustration of the thread type data for theexemplary compact email threads of FIGS. 9 and 10.

FIG. 13 is a block diagram illustration of the details of the indexer ofFIG. 5;

FIGS. 14 and 15 are graphical illustrations of exemplary posting listsof the index of FIG. 13;

FIG. 16 is a block diagram illustration of the details of the querymanager of FIG. 5;

FIG. 17 is a block diagram illustration of the initial steps of anexemplary candidate enumeration and verification process, introduced inFIG. 16;

FIG. 18 is a flow chart illustration of the candidate enumeration andverification process of FIG. 16;

FIG. 19 is a block diagram illustration of the details of an alternativeembodiment of the query manager of FIG. 5; and

FIG. 20 is a pseudocode illustration of the virtual cursor algorithmsemployed by the virtual cursor layer of FIG. 19.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

SUMMARY OF THE INVENTION

The present invention provides a novel method of indexing and searchinglarge volumes of electronic message transmissions (EMTs).

There is therefore provided, in accordance with a preferred embodimentof the present invention, a search engine including a compacting indexerand a query manager. The compacting indexer indexes well-ordered threadsof electronic message transmissions (EMTs). The query manager searchesthrough an index produced by the compacting indexer and identifies atleast one qualifying EMT of a qualifying EMT thread as a search resultwhen provided with a query.

Moreover, in accordance with a preferred embodiment of the presentinvention, the compacting indexer includes a thread processor todetermine the configurations of the EMT threads and to generate acompact EMT volume for indexing into an index.

Further, in accordance with a preferred embodiment of the presentinvention, the thread processor includes a docID assigner, a compact EMTcompiler and a thread configuration data compiler. The docID assignerassigns consecutive numerical IDs to the EMTs from meta-data associatedwith the EMTs. The compact EMT compiler generates a compact EMT for eachnumerical ID which is formed of the meta-data of the EMT and new contenttext added by the EMT to its thread. The thread configuration datacompiler compiles thread configuration data for the EMT threads.

Still further, in accordance with a preferred embodiment of the presentinvention, the thread configuration data compiler includes a root EMTdeterminer and a last offspring determiner. The root EMT determinerdetermines a root EMT of the EMT thread. The last offspring determinerdetermines a last offspring EMT of each EMT belonging to the EMT thread.

Additionally, in accordance with a preferred embodiment of the presentinvention, the thread configuration data compiler also includes a threadtype determiner to determine a thread type of each EMT thread.

Further, in accordance with a preferred embodiment of the presentinvention, the query manager includes a candidate enumerator, a postingsiteration manager and an assessment unit. The candidate enumeratorselects a candidate EMT for examination with respect to terms of thequery and the EMT thread configurations. The postings iteration managersearches posting lists of the index for the terms. The assessment unitassesses the multiple qualifying EMTs against the query.

Further, in accordance with a preferred embodiment of the presentinvention, the assessment unit includes a candidate ranker whichprovides, per qualifying EMT thread, at least one qualifying EMT as asearch result to the query according to a variable retrieval policy ofthe search engine. The retrieval policy is defined by the search engineor the user.

Further, in accordance with a preferred embodiment of the presentinvention, the retrieval policy dictates that the search result iseither the chronologically first qualifying EMT in each qualifying EMTthread, the chronologically last qualifying EMT in each qualifying EMTthread, the highest scoring qualifying EMT in each qualifying EMT threador all of the qualifying EMTs.

Alternatively, in accordance with a preferred embodiment of the presentinvention, the query manager includes a query processor and a virtualcursor layer. The query processor includes a postings iteration managerand an assessment unit. The query processor searches the posting listsof the index for the terms of the query. The assessment unit assessesthe multiple qualifying EMTs against the query. The virtual cursor layerguides a candidate enumeration process to enumerate candidate EMTs withrespect to the terms of the query and the EMT thread configurations.

Moreover, in accordance with a preferred embodiment of the presentinvention, the assessment unit includes a candidate ranker whichprovides, per qualifying EMT thread, at least one qualifying EMT as asearch result to the query according to a variable retrieval policy ofthe search engine. The retrieval policy is defined by the search engineor the user.

Further, in accordance with a preferred embodiment of the presentinvention, the retrieval policy dictates that the search result iseither the chronologically first qualifying EMT in each qualifying EMTthread, the chronologically last qualifying EMT in each qualifying EMTthread, the highest scoring qualifying EMT in each qualifying EMT threador all of the qualifying EMTs.

There is also provided, in accordance with a preferred embodiment of thepresent invention, a method including representing an unmodified volumeof EMT threads as a compact EMT volume, indexing the compact EMT volumeinto an index, searching the index, and returning EMT results from theunmodified volume.

Moreover, in accordance with a preferred embodiment of the presentinvention, the representing step includes associating, with a unique IDnumber assigned to each EMT in the unmodified volume, meta-data of theEMT and new content text added by each the EMT to its thread.

Further, in accordance with a preferred embodiment of the presentinvention, the indexing step includes distinguishing between occurrencesof a term in the EMT meta-data and in the EMT content.

Still further, in accordance with a preferred embodiment of the presentinvention, the method also includes determining thread configurationdata describing the EMT threads, and the searching step includessearching the index with the thread configuration data.

Additionally, in accordance with a preferred embodiment of the presentinvention, the determining step also includes analyzing the EMT threadsto identify a root EMT of each EMT thread and a last offspring EMT ofeach EMT. The root EMT is the source EMT spawning the EMT thread. Thelast offspring EMT is the EMT having the highest the numerical ID of allEMTs referring to the EMT.

Additionally, in accordance with a preferred embodiment of the presentinvention, the searching step includes identifying, as a candidate EMT,an EMT which appears in a posting list of the index of a required queryterm, verifying the occurrences of all remaining required terms of thequery in the content, the meta-data or ancestor content of the candidateEMT, verifying the absence of all forbidden terms of the query in thecontent, the meta-data and the ancestor content and advancing allposting lists of the index past invalid EMTs to select additionalcandidate EMTs.

Further, in accordance with a preferred embodiment of the presentinvention, the advancing step includes interpreting thread configurationdata to determine the identities of the invalid EMTs.

Further, in accordance with a preferred embodiment of the presentinvention, the returning step includes choosing at least one qualifyingEMT per qualifying EMT thread, which meets the query terms.

There is also provided, in accordance with a preferred embodiment of thepresent invention, a method including storing information describingconfigurations of discussion threads of EMTs, compacting the EMTdiscussion threads and indexing the compacted EMT discussion threadsgenerated by the compacting.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Applicants have realized that a significant portion of the volume ofemail messages in an email management system may be largely due to therepetition of messages in threaded discussions. Applicants have realizedthat similar threaded discussions are also common in newsgroups. Thepresent invention may be operable for all systems which have threadeddiscussions.

Applicants have further realized that for well-ordered threads, thepattern in which messages are repeated is typical, as shown in FIG. 1. Awell-ordered email discussion thread may be defined as one in which eachemail in the thread may contain the full content of its predecessor,i.e., the email preceding it in the thread, with no omissions oradditions. Applicants have realized that the predictability of thisrepetition may be exploited when processing a volume of emails, so thatportions of text that are repeated numerous times in successive emails,may be processed only once, rather than the multiple times they appear.This may result in a reduced volume of text to be processed.

Reference is now made to FIGS. 2, 3 and 4 in which exemplary, detailedversions of emails 10, 11 and 12 comprising email exchange 19 introducedin FIG. 1 are shown. As shown in FIG. 2, exemplary email 10 containsboth text 20, composed by the sender of email 10 to convey a message,and header 30, which may list some or all of the meta-data M₁₀associated with email 10. Email meta-data is a record of information,logged by the email servers handling the email, regarding the sender,recipient, subject and chronology of the email. Email servers handling avolume of emails, such as the g-mail server administered by Google, maytrack the meta-data of all emails sent and received by the server. Emailmeta-data may include the names and email addresses of the email senderand the email recipient, the date and time the email was sent, and thesubject of the email. This information may be stored in data fields‘From’, ‘From-email’, ‘To’, ‘To-email’, ‘Date’ and ‘Subject’respectively.

Electronic messages in general, of which email is one type, and of whichnewsgroup postings are another type, may have meta-data associated witheach message transmission, as recorded by the server sending andreceiving the messages.

Returning now to FIG. 2, meta-data M₁₀ indicates that on Wednesday, Oct.6, 2004, at 5:29 PM, email 10, regarding the bus schedule between SanFrancisco and Monterey, was sent by Bonnie Temple, from email addressbtemple@email.com, to the email address calitours@email.com. Header 30lists some of the meta-data M₁₀ information as text in email 10. Themessage conveyed by Bonnie Temple in content text 20 is an inquiry, forthe purpose of an upcoming trip to California, about the bus schedulebetween the two subject California locations.

FIG. 3 shows email 11, which includes both reply text 21 and rootmessage text 20, as explained in the background. The new content ofemail 11, i.e. reply text 21, is a response to Bonnie from Nelly ofCalitours Inc. providing the bus schedule information requested byBonnie. The meta-data of email 11, M₁₁, indicates that on Wednesday,Oct. 6, 2004, at 7:06 PM, email 11, regarding the bus schedule betweenSan Francisco and Monterey, was sent by Calitours, from email addresscalitours@email.com to Bonnie Temple, at the address btemple@email.com.Meta-data M₁₁ may include a complete record regarding the sender,recipient, subject and chronology of email 11, even though, as shown inFIG. 3, email 11 does not contain a header listing this information asin email 10. It is also noted that the appearance of the term “Re:” inthe Subject field indicates that email 11 refers to a previous messagehaving the subject “Bus schedule between San Francisco and Monterey”.

FIG. 4 shows email 12 which includes second reply text 22 in addition tofirst reply text 21 and root message text 20. The content of reply text22 sent by Bonnie to Nelly conveys her gratitude for the informationprovided by Nelly. Meta-data M₁₂ indicates that on Thursday, Oct. 7,2004, at 11:35 AM, email 12, regarding a previous message regarding thebus schedule between San Francisco and Monterey, was sent by BonnieTemple, from email address btemple@email.com, to Calitours, at the emailaddress calitours@email.com. Header 32 lists all of meta-data M₁₂ astext in email 12.

As may be seen, in an email volume containing emails 10, 11 and 12, text20 occurs three times, text 21 occurs two times, and text 22 occursonce. The present invention may be a search engine which may generallyconserve email administration system resources by exploiting thestructure of email threads to index each of text sections 20, 21 and 22one time only. The search engine may also search the index and ranksearch results according to retrieval policies based on thesingularities of message thread structures, improving the effectivenessof the search and the quality of the results.

The search engine disclosed in the present invention may also beoperable for all other types of electronic message transmission (EMT)volumes which are comprised of discussion threads, such as newsgrouppostings.

A preferred embodiment of the present invention may be as shown in FIG.5, to which reference is now made, and may employ search engine 40 toanalyze, index and search a volume of EMTs 50 handled by EMT server 48,which may include any number of EMT discussion threads (edt₁ . . .edt_(n)). As shown in FIG. 5, search engine 40 may comprise a threadprocessor 42, an indexer 44, a thread management database 43, an index58 and a query manager 46. Search engine 40 may support “free-text”search queries 52 regarding EMT volume 50, and may provide searchresults 54 in accordance with retrieval policies based on thesingularities of EMT thread structures. Free text queries includeBoolean expressions on required and/or forbidden, regular and/orfielded, keywords and/or phrases. For example, a query on a volume ofmessages may dictate that a particular word or phrase appear in amessage. Query criteria may also forbid the inclusion of a certain wordor phrase. In the present invention, criteria may be set for the messageitself or for the fields comprising the meta-data of the message.

Returning now to FIG. 5, the EMTs comprising EMT volume 50 may begrouped into threads edt₁ . . . edt_(n) by EMT server 48 on the basis ofthe EMT meta-data logged by server 48. Server 48 may also discern,within an EMT belonging to a thread, between new text appearing in theEMT for the first time in the thread, and repetitions of text frompreceding messages, on the basis of the meta-data logged by server 48for the EMTs in the thread.

Thread processor 42 may analyze threads edt₁ . . . edt_(n) to ascertaintheir structures, assign identification numbers to each EMT, and compilethread structure reference tables, described in more detail hereinbelow,defining the structures of the EMT threads. Thread structure informationprocessed by thread processor 42 may be stored in thread managementdatabase 43. The output of thread processor 42 may be a compact EMTvolume 56, which may be smaller in size than original volume 50. Thereduced EMTs which form compact EMT volume 56 may consist of the newtext contribution of each EMT in a thread and its meta-data, and may notinclude repetitions of text from preceding EMTs in the thread. Indexer44 may create a traditional inverted index 58 for compact EMT volume 56.Query manager 46 may process queries 52 input into search engine 40 byaccessing thread management database 43 and index 58. Query manager 46may return search results 54 in response to query 52.

EMT threads edt₁ . . . edt_(n) may have characteristic structuralconfigurations, e.g. linear or conjoined. The exemplary email threadshown in FIG. 1 is a linear thread. Each message in a linear threadcontains the full text of all preceding messages in the thread. FIG. 6,to which reference is now made, shows an exemplary conjoined thread set.

As shown in FIG. 6, conjoined thread sets may occur when more than twopeople are involved in an electronic message discussion initiated by asingle root message. In the example shown in FIG. 6, root email 100 issent from John to Tom, but a copy is also sent to Sally. The copy sentto Sally precipitates a discussion between Sally and Tom which occurs inparallel with the discussion occurring between Tom and John, while theinitial email from which both discussions evolved remains root email100. Another branch to the tree is added when Tom copies his reply toJohn (email 102) to Mom, and Mom replies (email 104) to Tom.

In a conjoined thread set configuration, such as that depicted in FIG.6, discussions may split at any point, spinning off sub-threads. Aconjoined thread set may be defined as a set of threads all sharing thesame root message. Neither thread may be fully contained in the other,and beyond the common root message, the messages in the two threads maybe disjoint. A set of conjoined threads may be seen as a directed tree,rooted at the root message. The tree-like structure of the conjoinedthread set shown in FIG. 6 is emphasized graphically in FIG. 7,reference to which is now made. FIG. 7 shows that the exemplaryconjoined thread set of FIG. 6 is rooted at root email 100 and has threebranches concluding with emails 101, 103 and 104. The tree may be theunion of the linear graphs defined by the individual threads in theconjoined set. A linear thread may therefore be seen as special andsimple occurrence of a conjoined thread set.

Reference is now made to FIG. 8 which shows the operation of threadprocessor 42 in detail. Thread processor 42 may comprise a docIDassigner 60, a root lookup table compiler 62, a last offspring lookuptable compiler 64, a thread type determiner 65 and a compact EMTcompiler 66. Input 50 for thread processor 42 may be a collection of anynumber of EMT discussion threads (edt₁ . . . edt_(n)), including linearthreads (lt₁ . . . lt_(n)) and conjoined thread sets (ct₁ . . . ct_(n)).As shown in FIG. 8, the exemplary linear thread introduced in FIG. 1shall be referred to as thread lt₁ for the purposes of this discussion.Similarly, the exemplary conjoined thread set introduced in FIG. 6 shallbe referred to as thread ct₁.

For linear EMT threads lt₁ . . . lt_(n), docID assigner 60 may assignconsecutive numerical IDs (docIDs) to sequential EMTs on the basis ofdocument creation time stored in the EMT meta-data. For conjoined threadsets ct₁ . . . ct_(n), DocID assigner 60 may use Depth First Search(DFS) numbering, as is well known in the art, on the directed treeimplied by the thread-set, starting from the root document.

Root lookup table compiler 62 may analyze threads edt₁ . . . edt_(n) andmay compile a root lookup table 67 listing the root EMT docID for everyassigned docID. Last offspring lookup table compiler 64 may analyzethreads edt₁ . . . edt_(n) and may compile a last offspring lookup table68 listing the last offspring EMT docID for every assigned docID. Thelast offspring EMT of EMT X is defined as the EMT having the highestdocID of all EMTs of which X is an ancestor. Taken together, root lookuptable 67 and last offspring table 68 may effectively provide completestructural descriptions for all email threads edt₁ . . . edt_(n).

Thread type determiner 65 may then analyze the data in root lookup table67 and last offspring lookup table 68 to determine whether a group ofEMTs belonging to a thread edt_(i) form a linear thread lt_(i) or aconjoined thread set ct_(i). Thread type determiner 65 may compile thisinformation in thread type lookup table 69 in which the value “L”(linear) or “J” (conjoined) may be assigned to each Root docID in rootlookup table 67. Thread type determiner 65 may identify that a rootdocID is the root of a linear thread if the root docID is common to agroup of consecutive docIDs which also share a common Last OffspringdocID. Thread type determiner 65 may identify that a root docID is theroot of a conjoined thread set if the root docID is common to a group ofconsecutive docIDs which have differing Last Offspring docIDs.

It is noted that the thread type data may be joined, as shown by arrow61, to root lookup table 67 so that each docID in the system may beidentifiable as belonging to a linear thread or to a conjoined threadset.

Compact EMT compiler 66 may compile compact EMT volume 56 byassociating, with each assigned docID, the meta-data and the new textcontent associated with that docID.

Exemplary compact email volumes, 70 and 72, for exemplary linear andconjoined email threads lt₁ and ct₁ respectively, are shown in FIG. 8.It may be seen that the compact emails constituting compact emailvolumes 70 and 72 may be comprised of the email meta-data and newcontent text associated with each email docID. For example, it is shownin FIG. 8 that compact email 10 may comprise the meta-data associatedwith email 10, indicated by the notation M₁₀, and text 20, the new textcontribution in email 10. The contents of compact emails 11, 12, 100,101, 102, 103 and 104 are similarly indicated in FIG. 8.

The reduction in volume realized by compact EMT compiler 66 may be seenby comparing the original volumes of email threads lt₁ and ct₁ andcompact volumes 70 and 72, respectively, represented graphically in FIG.8. Compact email volumes 70 and 72 may comprise only one copy of eachnew message text portion, rather than the multiple repetitions of thetext portions occurring in the non-compacted email threads.

Detailed representations of compact email volumes 70 and 72 are shown inFIGS. 9 and 10 respectively, reference to which is now made. Compactemail volume 70 for linear message thread lt₁, as shown graphically inFIG. 8, and in detail in FIG. 9, may include the meta-data of emails 10,11 and 12 (M₁₀, M₁₁ and M₁₂), and only the new message content of eachemail, i.e. one copy of message text portions 20, 21 and 22,respectively. A significant reduction in indexed message volume may thusbe achieved by the present invention, as the original volume of messagethread lt₁ may include three copies of text portion 20, two copies oftext portion 21 and one copy of text portion 22 as shown in FIG. 8.

Similarly, compact email volume 72 for conjoined thread ct_(1,) as showngraphically in FIG. 8, and in detail in FIG. 10, may include themeta-data of emails 100-104, (M₁₀₀, M₁₀₁, M₁₀₂, M₁₀₃, and M₁₀₄), andonly the new message content of each email, i.e. one copy of messagetext portions 90-94 respectively. A significant reduction from theoriginal volume of message thread ct₁, which may include five copies oftext portion 90, three copies of text portion 92 and one copy each oftext portions 91, 93 and 94, as shown in FIGS. 6 and 8, is thusrealized.

Reference is now made to FIGS. 11 a and 11 b which show the root andlast offspring lookup data for email threads lt₁ and ct₁ respectively.Root lookup table 74 for linear thread lt₁ and root lookup table 76 forconjoined thread ct₁ are shown separately in FIGS. 11 a and 11 brespectively for the sake of clarity, although as described in FIG. 8,all root lookup data for an entire email volume may be compiled in onetable in a preferred embodiment of the present invention. Similarly, alllast offspring lookup data for an email volume may be compiled in onetable in a preferred embodiment of the present invention. For the sakeof clarity however, the last offspring data for threads lt₁ and ct₁ arepresented separately in tables 75 and 77 in FIGS. 11 a and 11 brespectively.

A cursory review of these four tables may indicate how the structures ofboth linear and conjoined threads, and the distinction between them, maybe completely described by the combination of root lookup table 67 andlast offspring lookup table 68. Out of a volume of random emails 50, athread may be distinguished as a group of emails having the same rootemail, such as emails 10, 11 and 12 all sharing root email 10 as shownin table 74 of FIG. 11 a, and such as emails 100-104 all sharing rootemail 100 as shown in table 76 of FIG. 11 b. Accordingly, for a rootlookup table having thousands of entries for an email server volume 50,all docIDs sharing the same root may belong to one thread.

Last offspring lookup table 68 may provide the information necessary todistinguish linear threads from conjoined thread sets. A group ofconsecutively numbered emails which share their root email and theirlast offspring email is defined as a linear thread. As shown in FIG. 11a, email thread lt₁ meets this criteria, since all emails 10-12 in thethread share root email 10 and last offspring email 12. As shown in FIG.11 b, email thread ct₁ does not meet this criteria. While emails 100-104share root email 100, there are three different last offspring docIDsamong them. The last offspring of email 101 is email 101, the lastoffspring of email 103 is email 103, and the last offspring of emails100, 102 and 104 is email 104. A group of consecutively numbered emailswhich have a common root email, but a variety of last offspring isdefined as a conjoined thread set. Returning briefly to FIG. 7, wherethe three branches of conjoined thread ct₁, correlating to lastoffspring emails 101, 103 and 104, are depicted graphically, it is shownthat the number of unique last offspring docIDs for a conjoined threadset equals the number of branches in the thread.

Reference is now briefly made to FIG. 12 which shows thread type lookuptable 73 for exemplary email threads It₁ and ct₁. In table 73 the rootdocID of each thread and its associated thread type are tabulated. Theassociated thread type for exemplary linear thread lt₁ whose root docIDis 10, is shown to be “L” (linear), and the associated thread type forexemplary conjoined thread ct₁ whose root docID is 100, is shown to be“J” (conjoined).

As explained previously in the discussion of FIG. 8, the thread typedata in table 73 may alternatively be joined to root lookup table 67. Asshown in FIG. 12, table 74′ shows root lookup table 74 of FIG. 11 aaugmented with thread type data. Table 76′ similarly shows root lookuptable 76 of FIG. 11 b augmented with thread type data.

Reference is now made to FIG. 13 which shows the operation of indexer 44in detail. Indexer 44 may generate an inverted index 58 for compact EMTvolume 56. The output of indexer 44 may comprise posting lists 78 forunique words (tokens) T₁ through T_(i) appearing in both the content andthe meta-data of the compacted EMTs comprising compact EMT volume 56.Each posting list 78 may store an ordered set of posting entries 79where each entry may indicate the docID in which the token appeared, thespecific location of the token within the meta-data or content, andwhether the token appeared in the meta-data (“M”) or in the content(“C”) of the EMT. This information may be recorded as a triplet (docID,location, meta or content).

The value recorded in the second field indicating the location of thetoken in the docID may refer to a word count position in the meta-dataof the EMT if the value in the third field is an “M”, or to a word countposition in the content of the EMT if the value in the third field is a“C”.

Reference is now made to FIGS. 14 and 15 which show exemplary postinglists 78 for compact email volumes 70 and 72 shown in FIGS. 9 and 10 forexemplary email threads It₁ and ct₁ respectively. In FIG. 14, postinglist 80 shows posting entries for the token “Monterey”. Posting list 81shows posting entries for the token “December”, posting list 82 for thetoken “you”, and posting list 83 for the token “btemple@email.com”appearing in the From-email field of the email meta-data. The threevalues (10, 25, C) recorded in exemplary posting entry 88, indicate thatthe token ‘Monterey’ appears in docID number 10, in word position number25 of the message content as can be seen in FIG. 9. The three values(12, 3, M) recorded in exemplary posting entry 89, indicate that thetoken ‘<btemple@email.com>’ appears in word position number 3 after thecolon sign following the ‘From:’ field in the meta-data of docID number12 as can also be seen in FIG. 9.

In FIG. 15, exemplary posting lists 85, 86 and 87 list posting entriesfor the tokens “Tom”, “John” and “Mom”, respectively, as they appear incompact email volume 72 of FIG. 10.

Reference is now made to FIG. 16 which describes the operation of querymanager 46 in detail. Query manager 46 may utilize the information aboutthe thread structures stored in thread management database 43 to processuser-input queries 52 regarding EMT volume 50 in a generally more timeand resource efficient manner than if volume 50 were searched as anassortment of random unrelated text. The information about the EMTthread structures stored in thread management database 43 may organizeEMT volume 50 into its component threads, and query manager 46 maynavigate among these threads using the thread structure information as amap as discussed in further detail in FIGS. 17 and 18. Owing to the mapprovided by the thread structure information, query manager 46 mayconduct selective searches of EMT volume 50. For example, in the presentinvention, query manager 46 may anticipate that a forbidden term foundin a root email may appear in all subsequent emails in the thread andthus, the subsequent emails may all be disqualified immediately withoutbeing searched. Query manager 46 may anticipate these and otherparticularities of threaded EMT discussions, and may exploit them tooptimize the efficiency of the searching, scoring and ranking processes.

Query manager 46 may accomplish the task of guided systematic andselective searching of EMT volume 50, by beginning at a certain startpoint, i.e., by selecting one message candidate, and then, in aniterative process, using the rules and conditions prescribed in thealgorithms disclosed hereinbelow to validate or disqualify thatcandidate, and to determine the next candidate to be checked. Querymanager 46 may conserve system resources by skipping around messagevolume 50 to select candidates as dictated by the thread-savvyalgorithms.

In accordance with a preferred embodiment of the present invention,query manager 46 may conduct a selective, time and resource efficientsearch of a message volume 50 as described above without any loss ofrecall, that is, without failing to retrieve qualifying results to aquery due to the shortcuts taken in the indexing and search processes.

Returning now to FIG. 16, query 52 may consist of required terms R₁ . .. R_(n), forbidden terms F₁ . . . F_(n) and optional terms O₁ . . .O_(n). Generally speaking, an email may not be a qualifying result inresponse to query 52 if it does not contain appearances of requiredterms R₁ . . . R_(n). An email may also not be a qualifying result inresponse to query 52 if it contains an appearance of any forbidden termF₁ . . . F_(n). An email not disqualified for containing forbidden termsand containing any of optional terms O₁ . . . O_(n) may be more likelyto be returned as a result response to query 52 than an email notcontaining any of optional terms O₁ . . . O_(n).

As shown in FIG. 16 query manager 46 may comprise a postings iterationmanager (PIM) 120, a candidate enumerator (CE) 122, a candidate scorer124 and a candidate ranker 126.

Candidate enumerator 122 may employ postings iteration manager 120 in aniterative process in which, at any given time, one docID, theCandidateMessage, may be under consideration for qualifying as a searchresult for query 52. Postings iteration manager 120 may traverse postinglists PL₁ . . . PL_(n) of required terms R₁ . . . R_(n,) optional termsO₁ . . . O_(n) and forbidden terms F₁ . . . F_(n) of query 52. Candidateenumerator 122 may maintain three message pointers-CandidateMessage,CandidateRoot, and LastOffspring. The pointer CandidateMessage may pointto the document ID docID_(i) under consideration for candidacy as aresponse to query 52 at any given time. The pointer CandidateRoot maypoint to the root docID of docID_(i), and the pointer Last Offspring maypoint to the last offspring docID of docID_(i). The iterative process ofcandidate enumeration and examination for qualification performed by CE122 and PIM 120 is discussed in greater detail with respect to FIGS. 17and 18.

A message meeting the search criteria, i.e. a qualifying candidateQC_(i), may proceed to candidate scorer 124 for scoring. Qualifyingcandidates QC₁ . . . QC_(n) and their associated scores, ScQC₁ . . .ScQC_(n) may proceed to candidate ranker 126 for ranking.

Candidate scorer 124 may assign scores to qualifying candidates QC₁ . .. QC_(n), with ‘better’ candidates receiving higher scores. For example,a candidate email containing a certain number of optional terms O₁ . . .O_(n) may be assigned a higher score than a candidate email containing alesser number of optional terms O₁ . . . O_(n). Candidate ranker 126 mayassess the candidate scores on the basis of the retrieval policies ofsearch engine 40, and may assess which qualifying candidates may bereturned by the search engine as results to query 52. The retrievalpolicies of search engine 40 may be system or user defined.

Reference is now made to FIGS. 17 and 18, which describe the iterativeprocess of candidate enumeration and verification performed by CE 122and PIM 120. FIG. 17 provides an example for the initial steps of theprocess. FIG. 18 is a flowchart which describes a complete cycle of theprocess from nomination through validation of a candidate message.

In the example shown in FIG. 17, query 52 may contain required terms R1,R2 and R3. Postings iterator PI_(R1) may traverse the posting list forterm R₁ (PL_(R1)), postings iterator PI_(R2) may traverse the postinglist for term R₂ (PL_(R2)) and postings iterator PI_(R3) may traversethe posting list for term R₃ (PL_(R3)). In the first step of the process(step G1 in FIG. 18), posting iterator PI_(R1) may select the firstoccurrence OC_(R1) of required term R₁. In the example shown in FIG. 17,OC_(R1) is located at posting entry (PE) 152. Upon the selection ofoccurrence OC_(R1) by postings iterator PI_(R1), candidate enumerator122 may enumerate docID 115 for candidacy and pointer CandidateMessagemay point to docID 115 (step G2 in FIG. 18).

Candidate enumerator 122 may then access root lookup table 67 todetermine the root of the candidate message (step G3 in FIG. 18). In theexample shown in FIG. 17, the root of the candidate message docID 115,is 100 according to root lookup table 67 as, in the example of FIG. 17,all docIDs numbered 100 to 199 in root lookup table 67 have root 100,all docIDs numbered 200 to 299 have root 200, etc. Pointer CandidateRootmay then point to the root of the candidate message, e.g. docID 100 inthe example of FIG. 17.

In a preferred embodiment of the present invention, candidate enumerator122 may consult root lookup table 67 to ascertain whether the candidatemessage is part of a linear or conjoined thread (step G4 in FIG. 18). Inthis embodiment, one process is provided for candidate messagesbelonging to linear threads (steps L1 through L6 in FIG. 18) and adifferent process is provided for candidate messages belonging toconjoined thread sets (steps J1 through J7 in FIG. 18) In anotherpreferred embodiment of the present invention, all candidate messagesmay be processed as conjoined thread sets. The conjoined thread setprocedure may be valid for both conjoined thread sets and linear threadssince a linear thread is a simple, special instance of a conjoinedthread set.

As shown in FIG. 18, candidate enumerator 122 may determine that acandidate message belongs to a linear thread (step L1), and begin theprocedure for checking a candidate message which belongs to a linearthread (step L2). Candidate enumerator 122 may then check if either oneof the following two conditions are true for an occurrence of each ofthe remaining required terms, R₂ . . . R_(n) on posting lists PL_(R2) .. . PL_(Rn) respectively, as located by PI_(R2) . . . PI_(Rn)respectively.

The two conditions may be:

-   -   La) The occurrence of the required term is a meta occurrence in        docID [CandidateMessage]; and    -   Lb) The occurrence of the required term is a content occurrence        in a docID in the range of {CandidateRoot . . .        CandidateMessage}.

These conditions imply that when the postings iterator of a posting listof a required term PI_(Ri) is on a message with docID X, all otherposting lists may be safely advanced to a position at or beyond Root [X]without any loss of recall.

Returning to the example shown in FIG. 17, CE 122 and PIM 120 may checkCandidateMessage 115 and CandidateRoot 100 against conditions La and Lb.To this end, CE 122 may examine the occurrence of required term R₂ atposting entry 154 on PL_(R2). Posting entry 154 indicates a contentoccurrence of required term R₂ in docID 100. Candidate enumerator 122may ascertain that occurrence 154 meets condition Lb above since theoccurrence of term R₂ at docID 100 is a content occurrence of therequired term in the range of {Root [X] . . . X}, that is, in the range{100 . . . 115}.

Candidate enumerator 122 may then consider occurrence 156, of requiredterm R₃ in docID 105, as located by postings iterator PI_(R3). However,since occurrence 156 is a meta-occurrence, it must fulfill condition La,and since the candidate message under consideration is docID 115 and notdocID 105, condition La is not satisfied. Condition Lb is also notsatisfied by occurrence 156 because condition Lb requires a contentoccurrence and not a meta occurrence. Postings iterator PI_(R3) may thenadvance to occurrence 158 of term R₃ on PL_(R3). This occurrence isfound to satisfy condition Lb because it is a content occurrence atdocID 105 falling in the required range of 100 to 115.

Returning now to FIG. 18, candidate enumerator 122 may proceed to stepL3 if it determines that every required term of query 52 meets one ofconditions La or Lb. Candidate enumerator 122 may proceed to step L4 andchoose a new candidate message if at least one required term of query 52does not meet condition La or Lb.

During step L3, CE 122 may determine if the candidate message underconsideration is limited to CandidateMessage, or if all docIDs in therange {CandidateMessage . . . LastOffspring[CMsg]} may also becandidates. The last offspring of the candidate message,LastOffspring[CMsg] may be determined by CE 122 either by accessing lastoffspring lookup table 68, or by finding the highest docID in rootlookup table 67 which has the same root as CandidateMessage. Referringbriefly to FIG. 17, it may be seen in last offspring lookup table 68that the last offspring of CandidateMessage 115 is docID 199, and thatthe highest docID in root lookup table 67 sharing root 100 withCandidateMessage 115 is docID 199.

Returning now to FIG. 18, CE 122 may consider all docIDs in the range{CandidateMessage . . . LastOffspring[CMsg]} if condition Lb in step L2applies to all required terms posting lists (i.e., a match with nometa-occurrences has been identified). In this case, it may beguaranteed that all messages in the thread whose docID is greater thanCandidateMessage may also be qualifying messages, due to the structuralnature of well-ordered threaded EMTs, dictating that an EMT X in athread, by definition, contains all of the content of the EMTs precedingit in the thread.

CE 122 may then proceed to verify (step L5) the absence of forbiddenterms in CandidateMessage or in the range {CandidateMessage . . .LastOffspring[CMsg]}. CE 122 may examine the occurrences of allforbidden terms F₁ . . . F_(n) which fall within the range[CandidateRoot, . . . CandidateMessage] to determine if CandidateMessageor ranges of messages in the thread to which CandidateMessage belongsmay be disqualified for containing forbidden terms. Candidate enumerator122 may disqualify candidate messages according to the following rules:

-   -   La_(F)) A ‘content’ type occurrence of any forbidden term F₁ . .        . F_(n) anywhere in range [CandidateRoot, . . .        CandidateMessage] may disqualify all the messages in the thread        whose docID is greater than or equal to CandidateMessage; and    -   Lb_(F)) A ‘meta’ type occurrence within CandidateMessage may        disqualify only CandidateMessage.

Candidate enumerator 122 may proceed to step LA and choose a newcandidate message if all candidate messages are disqualified in step L5for containing forbidden terms. Qualifying candidate messages notdisqualified for containing forbidden terms may proceed to candidatescorer 124 (step G5).

Candidate scorer 124 may assign scores to qualifying candidates on thebasis of all the occurrences of query terms R₁ . . . R_(n) and O₁ . . .O_(n) in the message by iterating through query term occurrences in therange [CandidateRoot, . . . CandidateMessage] of all term posting lists.All content occurrences in the range may contribute to the score of aqualifying candidate QC, but meta occurrences may only contribute to thescore of a qualifying candidate if they occur in the qualifyingcandidate itself.

Once candidate enumerator 122 verifies a qualifying candidate orcandidates, CE 122 may proceed to step L6. In step L6, candidateenumerator 122 may choose the next candidate message in consideration ofthe retrieval policy of search engine 40. For example, the retrievalpolicy of search engine 40 may dictate that it is sufficient to returnas search results, only the first message in each thread which satisfiesquery 52. In this case, after scoring one qualifying candidate,candidate enumerator may start searching for the next candidatebeginning from the next thread, i.e., candidate enumerator 122 may skipall messages in the thread of the current qualifying candidate.

Alternatively, if the retrieval policy of search engine 40 dictates thatall relevant messages in the thread should be returned as searchresults, the search may be continued from CandidateMessage+1. Thismethod may allow search engine 40 to easily identify the highest scoringmessage of the thread—all thread candidates may be enumeratedsequentially, since they may be indexed with consecutive docIDs.Furthermore, scores for successive docIDs in a thread may be computedsimply by candidate scorer 124 on the basis of the scores of precedingdocIDs, that is, according to a methodology based on the patterns of theemail thread, in the following way: It is assumed that the score S(k) ofmessage k was just computed by candidate scorer 124, and that the nextCandidateMessage may be k+j. Since the content of each message may befully contained in the text of the following messages, the score S(k+j)of message (k+j) may equal to:S(k+j)=S(k)+CS(k+1, . . . ,k+j)−MS(k)+MS(k+j)

where CS indicates the score contributed by content occurrences and MSindicates the score contributed by meta occurrences.

Returning now to step G4 in FIG. 18, candidate enumerator 122 maydetermine (step J1) that a candidate message belongs to a conjoinedthread set, and then begin the examination procedure. Candidateenumerator 122 may first access last offspring lookup table 68 todetermine (step J2) the last offspring of the candidate message. Then CE122 may proceed to step J3 and begin the verification process of thecandidate message, in which CE 122 may determine if either one of thefollowing two conditions are true for at least one occurrence of each ofthe remaining required terms, R₂ . . . R_(n) on posting lists PL_(R2) .. . PL_(Rn) respectively, as located by PI_(R2) . . . PI_(Rn)respectively.

The two conditions may be:

-   -   Ja) The occurrence of the required term is a meta-occurrence in        docID [CandidateMessage].    -   Jb) The occurrence of the required term is a content occurrence        in docID X where X≦CandidateMessage and LastOffspring        [X]≧CandidateMessage.

These conditions imply that when the postings iterator PI_(Ri) of aposting list PL_(Ri) of a required term R_(i) is on a message with docIDk, all other posting lists may be safely advanced to a positionsatisfying the following two conditions without any loss of recall:

-   -   I. at or beyond Root [k] but no later than k; and    -   II. the LastOffspring of the position to which the posting list        is advanced is not smaller than k.        When condition (I) holds, but condition (II) does not, (i.e., a        query term is in a position X greater than Root[k] but        LastOffspring[X}<k), the posting list of the term may be safely        advanced to a position beyond LastOffspring [X].

CE 122 may then proceed to step J4 if it determines that every requiredterm of query 52 meets one of conditions Ja or Jb. CE 122 may proceed tostep J5 and choose a new candidate message if at least one required termof query 52 does not meet condition Ja or Jb.

During step J4, CE 122 may determine if the candidate message underconsideration is limited to CandidateMessage, or if all docIDs in therange {CandidateMessage . . . LastOffspring[CMsg]} may also becandidates. CE 122 may consider all docIDs in this range if condition Jbin step J4 applies to all posting lists (i.e., a match with nometa-occurrences has been identified). In this case it may be guaranteedthat all messages in the thread whose docID is no larger thanLastOffspring [CandidateMessage] may also be candidates.

CE 122 may also use the following rule to improve searching efficiency:If an occurrence of a query term in docID X satisfiesCandidateRoot<X<CandidateMessage but LastOffspring[X]<CandidateMessage,the posting list of the term may be advanced to the docID numberedLastOffspring[X]+1.

Candidate enumerator 122 may then proceed (step J6) to verify theabsence of forbidden terms in CandidateMessage or in the range{CandidateMessage . . . LastOffspring[CMsg]}. CE 122 may examine theoccurrences of all forbidden terms F₁ . . . F_(n) that fall within therange [CandidateRoot, . . . CandidateMessage] to determine ifCandidateMessage or ranges of messages in the thread to whichCandidateMessage belongs may be disqualified for containing forbiddenterms. Candidate enumerator 122 may disqualify messages according to thefollowing rules:

-   -   Ja_(F)) A ‘content’ type occurrence of any forbidden term F₁ . .        . F_(n) at location X satisfying X≦CandidateMessage and        LastOffspring [X]≧CandidateMessage, may disqualify X and all its        offspring, i.e. all messages whose docID is between X and        LastOffspring [X] (inclusive).    -   Jb_(F)) A ‘meta’ type occurrence within CandidateMessage may        disqualify only CandidateMessage.

CE enumerator 122 may proceed to step J5 and choose a new candidatemessage if all candidate messages are disqualified in step J6 forcontaining forbidden terms. Qualifying candidate messages notdisqualified for containing forbidden terms may proceed to candidatescorer 124 (step G5).

Candidate score assessor 124 may assign scores to qualifying candidateson the basis of all the occurrences of query terms R₁ . . . R_(n) and O₁. . . O_(n) in the message by iterating through query term occurrencesin the range [CandidateRoot, . . . CandidateMessage], of all termposting lists. All content occurrences in docIDs whoseLastOffspring≧Candidate Message may contribute to the score of thequalifying candidate, but meta occurrences may only contribute to thescore of the qualifying candidate if they occur in the qualifyingcandidate itself.

Once candidate enumerator 122 verifies a qualifying candidate orcandidates, CE 122 may proceed to step J7. In step J7, candidateenumerator 122 may choose the next candidate message in consideration ofthe retrieval policy of search engine 40. For example, the retrievalpolicy of search engine 40 may dictate that it is sufficient to returnas search results, only the first message in each thread which satisfiesquery 52. In this case, after scoring one qualifying candidate,candidate enumerator may start searching for the next candidatebeginning from the next thread, i.e., candidate enumerator 122 may skipall messages in the thread of the current qualifying candidate, andbegin searching at the docID numbered LastOffspring[CandidateRoot]+1.

Alternatively, if the retrieval policy of search engine 40 dictates thatall relevant messages in the thread should be returned as searchresults, the search may be continued from CandidateMessage+1. Thismethod may allow search engine 40 to easily identify the highest scoringmessage of the thread set—all thread candidates may be enumeratedsequentially, since they may be indexed with consecutive docIDs. Forscoring, operations may depend on whether CandidateMessage+1 refers toCandidateMessage, (i.e., CandidateMessage is an ancestor ofCandidateMessage+1). If CandidateMessage+1 refers to CandidateMessage,scores for successive docIDs may be computed simply by candidate scorer124 as described previously for linear threads.

However, if the last scored CandidateMessage has no offspring, theCandidateMessage counter may be advanced by one, and all posting listsmay be set to the root of the new CandidateMessage, in which case someposting lists may be rewound.

Alternatively, search engine 40 may follow a hybrid approach and mayreturn one message per qualifying thread in the thread set. This may beachieved by advancing the next candidate toLastOffspring[CandidateMessage]+1.

In an additional preferred embodiment of the present invention,illustrated in FIG. 19, reference to which is now made, the thread-basedcandidate enumeration process performed jointly by candidate enumerator122 and postings iteration manager 120 in an iterative process asdescribed hereinabove, may be separated from the other query managerprocesses and may be performed by virtual cursor layer 130 as shown inFIG. 19. This embodiment may allow thread-aware searches to be conductedwithin query processors which have not been especially adapted to thisparticular type of search method, such as query processor 135 shown inFIG. 19.

Objects and processes illustrated in FIG. 19 which are analogous toobjects and processes illustrated in FIG. 16 are identified withcorresponding reference numerals. In both embodiments of the presentinvention, as shown in FIGS. 16 and 19, query 52 may comprise the inputfor query manager 46. In both embodiments, postings iteration manager120 may employ posting iterators, also known in the art as physicalindex cursors, for each query term as shown in FIG. 17. However, whilepostings iteration manager 120 and candidate enumerator 122 may work intandem, as shown in FIG. 16 and as described hereinabove, to perform theprocess of candidate enumeration, FIG. 19 shows how virtual cursor layer130, in accordance with an additional preferred embodiment of thepresent invention, may serve as an intermediary between postingsiteration manager 120 and thread management database 43, directingselection of candidate EMTs by the posting iterators within postingsiteration manager 120. Postings iteration manager may thus be containedwithin a query processor 135, as shown in FIG. 19, which may be separatefrom virtual cursor layer 130, and which may not be specially adapted toconduct thread-aware query processing.

Virtual cursor layer 130 may operate as if it were superimposed over theposting iterators within postings iteration manager 120. Virtual cursorlayer 130 may thus provide knowledge of the thread structure of the EMTvolume being queried, as described by the data stored in threadmanagement database 43, which may include root lookup table 67 and lastoffspring table 68 (FIG. 16), to the underlying posting iterators. Thecandidate enumeration process conducted by the posting iterators maythus, as in the embodiment of the present invention illustrated in FIG.16, be steered according to the peculiarities of the EMT volume threadstructure.

The employment of virtual cursor layer 130 may isolate the query processfrom the EMT volume thread structure model, and may thus allow the EMTvolume thread structure model to be used in a query process while thequery process may remain oblivious to the details of the threadstructure and its implementation in candidate enumeration. Thisembodiment of the present invention may thereby allow thread-awaresearches to be conducted within query processes which have not beenspecially adapted to this particular type of search method.

Virtual cursor layer 130 may be provided by creating a “positive”virtual cursor for each required term, and a “negative” virtual cursorfor each forbidden term in query 52. Algorithms may be provided for thepositive and negative versions of two basic cursor methods next( ) andfwdBeyond( ), as well as for the method fwdShare( ). These algorithms,PositiveVirtual::next ( ), PositiveVirtual::fwdBeyond ( ),NegativeVirtual::next ( ), NegativeVirtual::fwdBeyond ( ) andPhysical::fwdShare ( ) may dictate the movements of the virtual cursorsand the underlying posting iterators, thereby enumerating candidateEMTs. Pseudocode for the algorithms is shown in FIG. 20, reference towhich is now made.

Algorithms 140, 142, 144, 146 and 148 shown in FIG. 20 describe acandidate enumeration procedure which is similar in principle to theprocedure explained hereinabove with respect to FIGS. 16 and 17. Bothcandidate enumeration procedures utilize the EMT thread structuredescription data to dictate the movement of the posting iterators sothat the query process may be conducted in a more efficient manner thanwould be possible without the data, as explained hereinabove withrespect to FIGS. 16 and 17.

In the algorithms shown in FIG. 20, THIS.DOCID corresponds to thecurrent position of the virtual cursor, and the term C_(P) correspondsto the underlying physical cursor. Algorithm 140, for positive next( ),forwards the virtual cursor for term Ti to the next docID that containsterm Ti. When C_(P) is on a shared posting, all of the offspring ofC_(P), which inherit term Ti from C_(P), are enumerated, as shown inlines 2-4 of the pseudocode, before C_(P) is physically moved, in line 7of the pseudocode.

Algorithm 142, for positive fwdBeyond(d), as shown in FIG. 20, forwardsthe virtual cursor to the next docID at or beyond docID D which containsterm Ti. This algorithm may rely on the physical cursor method fwdshare() to do most of its work. The call to CP.fwdShare(d), in line 6 ofalgorithm 142, attempts to position CP on the next document that sharesterm Ti with docID D. If there is no such document, fwdshare( ) returnswith CP positioned on the first document beyond d.

Algorithm 144, for negative next( ), as shown in FIG. 20 forwards thevirtual cursor to the next document not containing term Ti. It works bystriving to keep CP positioned ahead of the virtual cursor. Thedocuments d ε {THIS.DOCID, . . . CP−1}, which do not contain the term,may be enumerated until the virtual cursor catches up to CP, as shown inline 4 of the algorithm. When that happens, the virtual cursor isforwarded past the offspring of CP, which inherit the term from CP, asshown in lines 5-9 of algorithm 144, after which CP is moved forward, asshown in line 10. These steps may be repeated until CP moves ahead ofthe virtual cursor again.

Algorithm 146, for negative fwdBeyond(d) forwards the virtual cursor tothe next docID at or beyond docID D that does not contain the term Ti.As shown in line 6 of algorithm 146 fwdShare(d) is called to position CPon the next docID which shares term Ti with docID D. Then, as shown inline 14, next( ) is called to position the virtual cursor on the nextdocument that does not contain term Ti.

Algorithm 148, for fwdShare(d) strives to forward the physical cursor sothat it shares term Ti with docID D. If there is no such document, itreturns with the cursor positioned on the first docID beyond D. This isaccomplished, as shown in line 1 of algorithm 148, by looping until thephysical cursor moves beyond D or to a posting that shares term Ti withdocID D. The movement of the physical cursor depends on where the cursorlies. As shown in FIG. 20, lines 5-7 of algorithm 148 pertain to thescenario in which the cursor lies outside of the entire conjoined threadset to which docID D belongs. Lines 9-11 of algorithm 148 pertain to thescenario in which the cursor lies within the conjoined thread set towhich docID D belongs but not within the linear thread to which docID Dbelongs. Lines 13-15.of algorithm 148 pertain to the scenario in whichthe cursor lies on a private posting, that is, a particular occurrenceof Ti which is not shared by any other docID. For example, allmeta-occurrences are private, as well as occurrences in a solitary EMTwhich is its own root and last offspring.

In the additional preferred embodiment of the present inventionillustrated in FIG. 19, candidate scoring and ranking may proceed asdescribed in FIG. 16.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A method comprising: representing an unmodified volume of electronicmessage transmission (EMT) threads as a compact EMT volume consisting ofa new text contribution of each EMT in a thread and its meta-data andexcluding repetitions of text from preceding EMTs in the thread;indexing said compact EMT volume into an index; searching said index;and wherein said searching comprises: identifying as a candidate EMT, anEMT which appears in a posting list of said index of a required queryterm, said candidate EMT having content and meta-data; verifying theoccurrences of all remaining required terms of said query in at leastone of said content, said meta-data and ancestor content of saidcandidate EMT; verifying the absence of all forbidden terms of saidquery in said content, said meta-data and said ancestor content; andadvancing all posting lists of said index past invalid EMTs to selectadditional said candidate EMTs; and returning EMT results from saidunmodified volume.
 2. The method according to claim 1 and wherein saidadvancing comprises interpreting thread configuration data to determinethe identities of said invalid EMTs.
 3. The method according to claim 1and wherein said returning comprises, per qualifying EMT thread,choosing at least one qualifying EMT meeting said query terms.
 4. Themethod according to claim 3 and wherein a quantity and type of saidqualifying EMTs is variable and is determined by at least one of asystem and a user definition.
 5. The method according to claim 4 andwherein said quantity and type of said qualifying EMTs is at least oneof the following: the chronologically first said qualifying EMT in eachsaid qualifying EMT thread; the chronologically last said qualifying EMTin each said qualifying EMT thread; the highest scoring said qualifyingEMT in each said qualifying EMT thread; and all said qualifying EMTs.